PROFILER SPECTRAL MOMENTS (WHAT IT MEASURES)

MOMENT

COMMENTS
Doppler Power Spectrum Only the full spectrum at on range gate in one beam for each 6 minute profile is archived.  This is due to data communication limitations.  The archived gate is cycled through all gates, hence each gate is archived every 21.6 hours.
Signal Power Measure of the amount of power returned to the profiler.  Note that profilers are not well calibrated, so it is not possible to derive a reflectivity value (Z) from S.  The profiler algorithms define S as the power contianed between the two Doppler frequencies that bracket the portion of the spectrum that includeds the dominant spectral peak.  Here is a schematic example.  Also, the high mode is 16dB more sensitive than the low mode.
Radial Velocity Is the first moment (mean) of the Doppler power spectrum.  Radial velocities are combined from the three beams to derived the horizontal winds, similar to the dual-Doppler technique for Doppler radars.  One must be careful since the radial velocity may be due to clear-air data  (Bragg Scattering) and/or precipitation (Rayleigh Scattering).  Here is an example showing a Doppler power spectrum with precip and clear-air return.  Vertical velocity is obtained from the vertically pointing beam.  The sign convention is that positive is downward.
Velocity Variance Interpreted in a similar manner as Doppler radar variance.  It's a measure of turbulence, and as we will discuss later, is used to distinguish between different precip types.